Academic Press Insight, 5 April 1999
by Diana Steele
The people of the Harrapan-Indus civilization, who lived in what is now northwestern India, flourished between 2600 and 2000 B.C. To probe the region's climate history, a team of geologists from Israel, the United States, and India used carbon-dating and chemical analysis to examine sediments from a now-dry lake, Lunkaransar, in the Thar Desert. As the level of the briny lake fell, salts and other minerals precipitated in distinct layers. "These lake sediments give a very high-resolution record of changing lake levels, which reflect changing amounts of precipitation in the region," says Lisa Ely, a geologist at Central Washington University in Ellensburg.
Ely and her colleagues found that the lake has been mostly dry for the last 5500 years. Before then, they found, the region was wet for 15 centuries--a period that ended a millennium before the Harrapan-Indus peoples began to prosper. But an arid climate by no means rules out a healthy civilization, notes Blair Kling, a historian at the University of Illinois, Urbana-Champaign. Even without plentiful rain, the Harrapan-Indus inhabitants, he says, could have depended on the Indus River for irrigation. Kling says there is evidence that a flood may have forced refugees into the cities around 1600 B.C., leading to overcrowding that could have played a role in the civilization's downfall.